The retrieval of an object at sea is a difficult task in anything but the most calm conditions. The task is made more difficult when the retrieval is attempted from another floating object such as a ship. The continuous movement of the water imparts motion to each vessel, and since the vessels will be of different mass and shape, the motion of the vessel to be recovered will be different from that of the ship. The differing motion of the two vessels makes capture very difficult without causing damage to either vessel.
Present techniques for the recovery of remotely operated vessels or submersibles to a mother ship involve the use of diver(s) equipped with wetsuit and breathing apparatus, usually using an inflatable boat, to physically attach the prime lift hook from the ship to the vessel to be recovered after initially restricting the vessel's movement by attaching messenger lines from the ship. With manned support vessels, the lifting lines must also be secured by hand.
To avoid danger to humans, the operations of vessel capture, lift and motion control are preferably done remotely.
Various systems have been proposed for the recovery of submersibles or other vessels. Examples of prior systems are disclosed in U.S. Pat. Nos. 3,807,335, 3,937,163, 3,955,522, and 4,516,517.
The existing systems are not entirely satisfactory in providing a simple system for launching and recovering a smaller vessel safely from a mother vessel.